Distinct patterns of vascular smooth muscle growth are associated with pathophysiologic states which impact on the kidney. In models of chronic hypertension, such as the spontaneously hypertensive rate (SHR), hypertrophy of vascular smooth muscle cells (VSMC) without any significant increase in cell number is observed. In atherosclerosis, the predominant event is hyperplasia of VSMC with little increase in cell size. These distinct patterns of growth are presumed to be a result of different stimuli acting on the cells. Distinct patterns of growth are also observed when cultured VSMC are stimulated. Vasoconstrictors such as arginine vasopressin (AVP) induce hypertrophy but not cell division when acting as slow stimuli. In contract polypeptide growth factors such as PDGF are complete mitogens and stimulate cell division. Both of these agents activate many of the same post-receptor signaling events. Thus the critical signalling mechanisms responsible for these disparate patterns of growth have not been established. VSMC in vivo exist in tow phenotypic states: a synthetic or proliferative phenotype, found in embryonic tissue, and a contractile phenotype found in vessels of adult animals. These phenotypic states can be distinguished morphologically, and by the selective expression of smooth muscle-specific actin isoforms. In atherosclerosis VSMC "de-differentiation" from the contractile to the proliferative phenotype precedes the onset of hyperplasia. Distinct phenotypic states have also been demonstrated in culture; VSMC grown on a support of laminin maintain the contractile phenotype, whereas cells grown on plastic maintain the proliferative phenotype. The central hypothesis of the proposed studies is that: the physiologic response of VSMC will be a function both of the phenotypic state of the vascular smooth muscle cells, and the particular stimulus. This proposal will compare receptor and post-receptor signaling events in VSMC following stimulation by AVP or PDGF. Activation of protein and kinases will be examined. We have recently developed a model for the two phenotypic states by growing cells on Matrigel, a synthetic matrix (contractile) or untreated plastic dishes (proliferative). Contractile VSMC are characterized by low proliferative rate, high levels of alpha-actin and hypercontraction compared to proliferative cells. Contractile cells also show a marked inhibition of agonist-induced mitogen-activated protein (MAP) kinase activity consistent with representing a non-proliferative population. The responses cells of each phenotype to AVP and PDGF will be examined. The role of G-proteins in mediating the effects of AVP will be examined by stably expressing mutant G-protein alpha-subunits. AVP and PDGF have been shown to have opposite effects on induction of smooth muscle alpha-actin, a marker for the contractile phenotype. Elements of the alpha-actin promoter responsible for agonist-induced and phenotypic- dependent expression will be identified. Finally, signalling in VSMC from SHR rats will be studied to define molecular events responsible for the observed hypertrophy of these cells. These studies will provide an understanding of the factors important for VSMC growth, contraction, and development.